U.S. patent number 8,709,282 [Application Number 13/500,450] was granted by the patent office on 2014-04-29 for process for producing .beta.-sialon fluorescent material.
This patent grant is currently assigned to Denki Kagaku Kogyo Kabushiki Kaisha. The grantee listed for this patent is Masayoshi Ichikawa, Hironori Nagasaki. Invention is credited to Masayoshi Ichikawa, Hironori Nagasaki.
United States Patent |
8,709,282 |
Ichikawa , et al. |
April 29, 2014 |
Process for producing .beta.-sialon fluorescent material
Abstract
Provided is a production method of a .beta.-type sialon
fluorescent substance, where luminescence intensity can be improved
without adding a metal element other than elements composing a
.beta.-type sialon fluorescent substance. Namely, in a production
method of a fluorescent substance containing an optically-active
element as the luminescence center in a crystal of nitride or acid
nitride, a .beta.-type sialon fluorescent substance is produced by
a burning process for heat-treating a mixture including metal
compound powder and an optically-active element compound; a
high-temperature annealing process for heat-treating the burned
product after cooling under a nitrogen atmosphere; a rare-gas
annealing process for heat-treating the high-temperature annealed
product under a rare gas atmosphere; and a process for treating the
rare-gas treated product with an acid.
Inventors: |
Ichikawa; Masayoshi (Tokyo,
JP), Nagasaki; Hironori (Tokyo, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Ichikawa; Masayoshi
Nagasaki; Hironori |
Tokyo
Tokyo |
N/A
N/A |
JP
JP |
|
|
Assignee: |
Denki Kagaku Kogyo Kabushiki
Kaisha (Tokyo, JP)
|
Family
ID: |
43969905 |
Appl.
No.: |
13/500,450 |
Filed: |
October 27, 2010 |
PCT
Filed: |
October 27, 2010 |
PCT No.: |
PCT/JP2010/069078 |
371(c)(1),(2),(4) Date: |
May 07, 2012 |
PCT
Pub. No.: |
WO2011/055665 |
PCT
Pub. Date: |
May 12, 2011 |
Prior Publication Data
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|
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Document
Identifier |
Publication Date |
|
US 20120211700 A1 |
Aug 23, 2012 |
|
Foreign Application Priority Data
|
|
|
|
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Nov 5, 2009 [JP] |
|
|
2009-254479 |
|
Current U.S.
Class: |
252/301.4F |
Current CPC
Class: |
C09K
11/0883 (20130101); C01B 21/0826 (20130101); C09K
11/7734 (20130101); C01P 2006/60 (20130101); C01P
2002/84 (20130101); C01P 2004/03 (20130101); C01P
2002/54 (20130101); C01P 2004/51 (20130101) |
Current International
Class: |
C09K
11/64 (20060101) |
Field of
Search: |
;252/301.4F |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1 964 905 |
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Sep 2008 |
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EP |
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2 093 272 |
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Aug 2009 |
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EP |
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10-036833 |
|
Feb 1998 |
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JP |
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2000-034477 |
|
Feb 2000 |
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JP |
|
2005-255885 |
|
Sep 2005 |
|
JP |
|
2005-255895 |
|
Sep 2005 |
|
JP |
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2008-050462 |
|
Mar 2008 |
|
JP |
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2008-255200 |
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Oct 2008 |
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JP |
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WO 2006/087661 |
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Aug 2006 |
|
WO |
|
Other References
International Search Report issued in International Application No.
PCT/JP2010/069078 on Dec. 21, 2010. cited by applicant .
European Search Report issued from the European Patent Office in
the corresponding European Application No. 10828225.2-1355 on Nov.
19, 2013. cited by applicant.
|
Primary Examiner: Koslow; Carol M
Attorney, Agent or Firm: Stein IP, LLC
Claims
The invention claimed is:
1. A production method of a .beta.-type sialon fluorescent
substance containing an optically-active element as a luminescence
center in a crystal of nitride or acid nitride: a burning process
for heat-treating a mixture including silicon nitride, aluminum
compound powder and an optically-active element compound; a
high-temperature annealing process for heat-treating the burned
product after cooling under a nitrogen atmosphere; a rare-gas
annealing process for heat-treating the high-temperature annealed
product under a rare gas atmosphere; and a process for treating the
rare-gas treated product with an acid.
2. A production method of a .beta.-type sialon fluorescent
substance containing an optically-active element as a luminescence
center in a crystal of nitride or acid nitride: a nitriding process
for heating a mixture including silicon, aluminum compound powder
and an optically-active element compound under a nitrogen
atmosphere; a burning process for heat-treating the nitrided metal
compound and the optically-active element compound; a
high-temperature annealing process for heat-treating the burned
product after cooling under a nitrogen atmosphere; a rare-gas
annealing process for heat-treating the high-temperature annealed
product under a rare gas atmosphere; and a process for treating the
rare-gas treated product with an acid.
3. The production method of a .beta.-type sialon fluorescent
substance according to claim 1, wherein a heat treatment
temperature in the high-temperature annealing process is lower than
a heating temperature in the burning process.
4. The production method of a .beta.-type sialon fluorescent
substance according to claim 1, wherein a heat treatment
temperature in the rare-gas annealing process is lower than a
heating temperature in the burning process.
5. The production method of a .beta.-type sialon fluorescent
substance according to claim 2, wherein a heat treatment
temperature in the high-temperature annealing process is lower than
a heating temperature in the burning process.
6. The production method of a .beta.-type sialon fluorescent
substance according to claim 2, wherein a heat treatment
temperature in the rare-gas annealing process is lower than a
heating temperature in the burning process.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a National Phase of PCT International Patent
Application No. PCT/JP2010/069078, filed Oct. 27, 2010, and claims
priority benefit to Japanese Patent Application No. 2009-254479,
filed Nov. 5, 2009, in the Japanese Patent Office, the disclosures
of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a production method of a
.beta.-type sialon fluorescent substance.
2. Description of the Related Art
Light-emitting devices combined with a light-emitting element
emitting a primary light and a fluorescent substance absorbing the
primary light and emitting a secondary light have been drawing
attentions as a next-generation light-emitting device being
expected to have low power consumption, miniaturization, high
brightness and extensive color reproducibility, and they have
actively been researched and developed.
For example, there is disclosed a white LED obtaining white light
by color mixture of light emitted by the semiconductor
light-emitting element and wavelength-converted light by the
fluorescent substance, by combining a semiconductor light-emitting
element emitting a visible light of short wavelength from blue to
purple with a fluorescent substance.
As output of a white LED increases, heat stability and durability
of a fluorescent substance have been demanded more than ever, and a
fluorescent substance which is low in deterioration of luminescence
intensity due to temperature rise and excellent in durability has
been required, so a fluorescent substance of nitride or acid
nitride typified by a .beta.-type sialon fluorescent substance
whose crystal structure is stable has been drawing attentions.
It has been known that a .beta.-type sialon fluorescent substance
is obtained by mixing silicon nitride (Si.sub.3N.sub.4), aluminum
nitride (AlN) and an optically-active element compound such as
europium oxide (Eu.sub.2O.sub.3) in a predetermined mole ratio,
then burning it at a temperature near 2000.degree. C., and grinding
the resulting burned product, or produced by further acid treatment
of the burned product obtained (Patent document 1).
However, since the .beta.-type sialon fluorescent substance
obtained by the above-described method is low in luminescence
intensity, in the case of a white LED obtained by combination with
a semiconductor light-emitting element, there is pointed out a
problem that the light-emitting efficiency is low.
In order to improve the luminescence intensity of a .beta.-type
sialon fluorescent substance, there is a proposition that before
burning, fluoride, chloride, iodide or bromide of an element
selected from Li, Na, K, Mg, Ca, Sr and Ba, or phosphate is added
(Patent document 2). This method aimed to improve reactivity in
burning and promote the growth of crystal grain by adding the
above-described compound.
CITATION LIST
Patent Literature
[PTL 1] Japanese Unexamined Patent Application Publication No.
2005-255885
[PTL 2] Japanese Unexamined Patent Application Publication No.
2005-255895
SUMMARY OF THE INVENTION
However, according to the method described in Patent document 2,
since metal elements other than elements composing a .beta.-type
sialon fluorescent substance are included in burning, it is pointed
out that formation of a hetero-phase different from .beta.-type
sialon crystal, such as .alpha.-type sialon crystal, tends to
occur. In particular, in the case that alkaline earth metals such
as Ca and Mg are included in burning, as a result, it cannot obtain
a sufficient improvement effect of luminescence intensity, which is
not preferable.
The present invention aims to improve luminescence intensity
without adding a metal element other than elements composing a
.beta.-type sialon fluorescent substance.
The present inventors have keenly studied for increasing the
luminescence intensity of a .beta.-type sialon fluorescent
substance, as a result, found out that the luminescence intensity
becomes strong by conducting a heat treatment under a nitrogen
atmosphere and a heat treatment under a rare gas atmosphere after
burning, and completed the present invention.
In a production method of a fluorescent substance containing an
optically-active element as the luminescence center in a crystal of
nitride or acid nitride, the present invention provides a
production method of a .beta.-type sialon fluorescent substance
comprising a burning process for heat-treating a mixture including
silicon nitride, aluminum compound powder and an optically-active
element compound; a high-temperature annealing process for
heat-treating the burned product after cooling under a nitrogen
atmosphere; and a rare-gas annealing process for heat-treating the
high-temperature annealed product under a rare gas atmosphere.
In a production method of a fluorescent substance containing an
optically-active element as the luminescence center in a crystal of
nitride or acid nitride, the present invention also provides a
production method of a .beta.-type sialon fluorescent substance
comprising a nitriding process for heating a mixture including
silicon, aluminum compound powder and an optically-active element
compound under a nitrogen atmosphere; a burning process for
heat-treating the nitrided metal compound and the optically-active
element compound; a high-temperature annealing process for
heat-treating the burned product after cooling under a nitrogen
atmosphere; a rare-gas annealing process for heat-treating the
high-temperature annealed product under a rare gas atmosphere; and
a process for treating the rare-gas treated product with an
acid.
In these production methods of a .beta.-type sialon fluorescent
substance, it is preferable that the heat treatment temperature in
the high-temperature annealing process is a temperature lower than
the heating temperature in the burning process. It is preferable
that the heat treatment temperature in the rare-gas annealing
process is a temperature lower than the heating temperature in the
burning process.
According to the production method of a .beta.-type sialon
fluorescent substance of the present invention, luminescence
intensity can be improved by heat treatments under a nitrogen
atmosphere and under a rare gas atmosphere after burning.
Further, the fluorescent substance of the present invention shows
an excellent characteristic in comparison with the conventional
.beta.-type sialon fluorescent substance in regard to brightness
and color reproducibility when used for a light source of back
light in an image display apparatus such as LCD. Such fluorescent
substance can be suitably used in a semiconductor light-emitting
device, and the semiconductor light-emitting device can be suitably
used in an image display apparatus.
Additional aspects and/or advantages of the invention will be set
forth in part in the description which follows and, in part, will
be obvious from the description, or may be learned by practice of
the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
These and/or other aspects and advantages of the invention will
become apparent and more readily appreciated from the following
description of the embodiments, taken in conjunction with the
accompanying drawings of which:
FIG. 1 is a flow diagram for explaining procedures in a production
method of a .beta.-type sialon fluorescent substance according to a
first embodiment of the present invention.
FIG. 2 is a flow diagram for explaining procedures in a production
method of a .beta.-type sialon fluorescent substance according to a
second embodiment of the present invention.
FIG. 3 is a diagram showing a scanning electron microscope (SEM)
picture of fluorescent substance powder ground by ultrasonic jet in
Example 1.
FIG. 4 is a diagram showing a scanning electron microscope (SEM)
picture of fluorescent substance powder after acid treatment in
Example 1.
FIG. 5 is a diagram showing a scanning electron microscope (SEM)
picture of fluorescent substance powder after acid treatment in
Comparative Example 1.
FIG. 6 is a graph showing the particle size distribution of
fluorescent substance powder in Example 1 and Comparative Example
1.
FIG. 7 is a graph showing the variation of crystal defects for each
process in Example 1 and Comparative Example 1.
FIG. 8 is a graph showing the luminescence intensity of fluorescent
substance powder in Example 1 and Comparative Example 1.
DETAILED DESCRIPTION OF THE EMBODIMENTS
Reference will now be made in detail to the present embodiments of
the present invention, examples of which are illustrated in the
accompanying drawings, wherein like reference numerals refer to the
like elements throughout. The embodiments are described below in
order to explain the present invention by referring to the
figures.
(First Embodiment)
The production method of a .beta.-type sialon fluorescent substance
according to a first embodiment of the present invention is
characterized by comprising a burning process for heat-treating a
mixture including silicon nitride, an aluminum compound and an
optically-active element compound; a high-temperature annealing
process for heat-treating the burned product after cooling under a
nitrogen atmosphere; and a rare-gas annealing process for
heat-treating the high-temperature annealed product under a rare
gas atmosphere. The outline of treatment flow is shown in FIG.
1.
The aluminum compound means at least one kind of aluminum compound
selected from aluminum nitride, aluminum oxide, or an
aluminum-containing compound producing aluminum oxide through
decomposition by heating.
The optically-active element compound is a compound of one kind, or
more than one kind of elements selected from the group consisting
of Mn, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, and Yb, and
preferably oxide thereof. These elements function as the
luminescence center and exhibit fluorescent characteristics. An
element commonly used as a fluorescent substance emitting yellow
light by irradiation of blue light is europium oxide.
The burning process is conducted by heating under a nitrogen
atmosphere or under a nonoxidative condition in accordance with
conditions of the standard method. The heating temperature is
preferably in a range of 1850 to 2050.degree. C. When a heating
temperature is not less than 1850.degree. C., Eu.sup.2+ can enter
into a .beta.-type sialon crystal, thereby a fluorescent substance
having sufficient luminescence intensity is obtained. When a
heating temperature is not more than 2050.degree. C., it is
industrially preferable because there is no need to restrain the
decomposition of .beta.-type sialon by loading a very high nitrogen
pressure, therefore no need for special equipment.
Next, after the burned product is cooled, it undergoes heat
treatment under a nitrogen atmosphere. Hereinafter, the heat
treatment under a nitrogen atmosphere after cooling is called a
high-temperature annealing process.
Cooling is slowly conducted in such a manner that the burned
product is allowed to stand until its temperature becomes room
temperature or lower. Without cooling, it is not possible to
improve the luminescence intensity of a .beta.-type sialon
fluorescent substance sufficiently.
The burned product becomes granular or clumpy, thus after cooling,
it may be converted to powder with a predetermined size by
crushing, grinding and/or combination with a classification
operation. As an example of the specific treatment, there is listed
a method that a burned product undergoes a sieve-classification
treatment in a range of 20 to 45 .mu.m opening to obtain powder
passed through the sieve, or a method that a synthetic is ground to
a predetermined particle size using a common grinder such as ball
mill, vibration mill and jet mill. In regard to grinding by a jet
mill, in the case of adopting an excessive treatment condition,
there is a case that crystal defects occur on the particle surface
causing the lowering of light-emitting efficiency. In the case of
using a grinder, it is preferable for the grinding condition to be
milder.
The heating temperature in the high-temperature annealing process
is preferably in a range of 1700 to 1900.degree. C. When the
heating temperature becomes not less than 1900.degree. C., it is
not preferable because of decomposition of .beta.-type sialon and
evaporation of Eu being the luminescence center. When the heating
temperature becomes not more than 1700.degree. C., it is not
preferable because crystallizability cannot be improved
sufficiently. The pressure condition is preferably 0.1 MPa or more.
In the case of 0.1 MPa or less, it is not preferable because
decomposition of .beta.-type sialon occurs.
After the high-temperature annealing process, a treated product
obtained in the high-temperature annealing process is subjected to
heat treatment under a rare gas atmosphere. This process is called
a rare-gas annealing process. The treated product in the
high-temperature annealing process is cooled to near room
temperature in the same manner as the burned product or powder of
the burned product, and subjected to heat treatment in the rare-gas
annealing process. Fluorescence characteristics are improved by
conducting the rare-gas annealing process along with the
high-temperature annealing process.
The heating temperature in the rare-gas annealing process is in a
range of 1300 to 1500.degree. C., and the range of 1300 to
1500.degree. C. is particularly preferable. When it is 1300.degree.
C. or more, destabilization of low crystalline part is possible,
and when 1500.degree. C. or less, it is possible to restrain the
decomposition of crystal structure of a .beta.-type sialon
fluorescent substance.
Regarding rare gas, there can be used one kind of gas selected from
He, Ne, Ar, Kr, Xe and Rn, or a mix gas of two kinds or more
thereof. In particular, Ar gas is preferable.
Based on the studies of the present inventors, the heat treatment
in rare gas anneal is a treatment for destabilizing a low
crystalline part in a fluorescent substance. By heat treatment in a
rare gas atmosphere, the low crystalline part is destabilized, and
this is removed by an acid treatment process of the next process.
Additionally, it is desirable that the particle size of powder is
sorted by a sieve before the acid treatment process.
Next, unstable low crystalline parts generated in the rare-gas
annealing process, and phases different from a .beta. sialon
fluorescent substance are treated with an acid, and removed
(hereinafter, referred to as an acid treatment process). Acid
treatment can be carried out by a heat treatment with a mix acid of
hydrofluoric acid and nitric acid, for example. Fluorescent
characteristics are greatly improved by removing low crystalline
parts. Regarding the heat treatment temperature, a dissolving
treatment by a mixture of hydrofluoric acid and nitric acid heating
at 60.degree. C. or more for 5 minutes or more is effective and
preferable.
Dispersion liquid of the .beta.-type sialon fluorescent substance
obtained by the acid treatment is washed with water and dried to
obtain fluorescent substance powder. Further, minute powders may be
removed by a wet precipitation method and the like of the
fluorescent substance powder.
(Second Embodiment)
The difference from the first embodiment is as follows: in the
second embodiment, silicon is used in place of silicon nitride, and
a nitriding treatment is conducted before burning a mixture
including at least one kind of aluminum compound selected from
aluminum nitride, aluminum oxide or an aluminum-containing compound
producing aluminum oxide through decomposition by heating, and an
optically-active element compound.
FIG. 2 shows the outline of treatment flow of a .beta.-type sialon
fluorescent substance according to the second embodiment of the
present invention. Namely, it is a production method of a
.beta.-type sialon fluorescent substance comprising a nitriding
process for heating a mixture including metal compound powder and
an optically-active element compound under a nitrogen atmosphere; a
burning process for heat-treating a nitrided metal compound and an
optically-active element compound; a high-temperature annealing
process for heat-treating the burned product after cooling under a
nitrogen atmosphere; a rare-gas annealing process for heat-treating
the high-temperature annealed product under a rare gas atmosphere;
and a process for treating the rare-gas treated product with an
acid.
The nitriding treatment process is a treatment for nitriding
silicon, and it may be conducted by heating under a nitrogen
atmosphere in accordance with nitriding treatment conditions of the
standard method. Namely, for converting silicon into
Si.sub.3N.sub.4 by nitriding, it is heated at 1200 to 1550.degree.
C. The heating temperature is preferably in a range of 1450 to
1500.degree. C. When the heating temperature is 1450.degree. C. or
more, Eu.sup.2+ can enter into a .beta.-type sialon crystal,
thereby obtaining a fluorescent substance having sufficient
luminescence intensity. When preheating temperature exceeds
1500.degree. C., luminescence wavelength of the fluorescent
substance finally obtained becomes long, and when pressure exceeds
0.5 MPa, luminescence wavelength of the fluorescent substance
finally obtained becomes long, which became clear from the research
of the present inventors. Therefore, it is preferable to be
conducted at 1500.degree. C. or less, and under a pressure
condition of 0.5 MPa.
The treatment conditions of the burning process, high-temperature
annealing process, rare-gas annealing process and acid treatment
are the same as those in the first embodiment. In the same way as
in the first embodiment, dispersion liquid of the .beta.-type
sialon fluorescent substance obtained by the acid treatment is
washed with water and dried to obtain fluorescent substance powder,
further, minute powders may be removed by a wet precipitation
method and the like of the fluorescent substance powder.
EXAMPLES
Hereinafter, the present invention will be described further in
detail based on Examples and Comparative Examples.
Example 1
(1) Preparation of Raw Material Powder for Eu-containing .beta.
Sialon
There were compounded 95.5 mass % of .alpha.-type silicon nitride
powder (manufactured by Ube Industries, Ltd., "SN-E10" grade,
oxygen content 1.1 mass %), 3.3 mass % of aluminum nitride powder
(manufactured by Tokuyama Corporation "F" grade, oxygen content 0.9
mass %), 0.4 mass % of aluminum oxide powder (manufactured by
Taimei Chemicals Co., Ltd., "TM-DAR" grade), and 0.8 mass % of
europium oxide powder (manufactured by Shin-Etsu Chemical Co.,
Ltd., "RU" grade), thereby obtaining a raw material mixture of 1
kg.
The raw material mixture was dry-mixed for 30 minutes using a
V-type mixing machine, further it was all passed through a sieve
made of nylon with 150 .mu.m opening to obtain raw material powder
for synthesizing a fluorescent substance.
(2) Burning Process
The raw material powder of 170 g was filled in a cylindrical
container made of boron nitride of inner diameter 10
cm.times.height 10 cm with a lid (manufactured by Denki Kagaku
Kogyo Kabushiki Kaisha, "N-1" grade), it was heat-treated in an
electric furnace with a carbon heater in a pressured nitrogen
atmosphere of 0.9 MPa at 2000.degree. C. for 15 hours, then the
resulting powder was slowly cooled to room temperature. The burned
product obtained was clumpy and loosely aggregated, and it was able
to be flaked gently by a hand wearing a clean rubber glove. In this
way, after being crushed to a slight degree, it was passed through
a sieve of 150 .mu.m opening. By these operations, synthesized
powder of 160 g was obtained.
The synthesized powder was crushed by an ultrasonic jet grinder
(manufactured by Nippon Pneumatic Mfg. Co., Ltd., PJM-80SP) to
obtain the ground powder. FIG. 3 shows a scanning electron
microscope (SEM) picture of the ground powder obtained.
Additionally, this grinder can control the particle diameter of the
ground powder by a sample-feeding speed into a grinding room and a
grinding air pressure.
(3) High-temperature Annealing Process
The ground powder of 70 g was filled in a cylindrical container
made of boron nitride of diameter 70 mm.times.height 45 mm with a
lid (manufactured by Denki Kagaku Kogyo Kabushiki Kaisha, "N-1"
grade), and it was heat-treated in an electric furnace with a
carbon heater in a pressured nitrogen atmosphere of 0.9 MPa at
1900.degree. C. for 8 hours. The resulting powder was all passed
through a sieve of 45 .mu.m opening.
(4) Rare Gas Process
The resulting powder of 15 g was filled in a cylindrical container
made of boron nitride of diameter 40 mm.times.height 45 mm with a
lid (manufactured by Denki Kagaku Kogyo Kabushiki Kaisha, "N-1"
grade), and it was heat-treated in an electric furnace with a
carbon heater in an argon atmosphere of atmospheric pressure at
1450.degree. C. for 8 hours. The resulting powder had no shrinkage
associated with burning, it was almost the same aspect as that
before heating, and all passed through a sieve of 45 .mu.m opening.
Additionally, in the following description, heat treatment using
argon gas in the rare gas process is called an argon annealing
process.
(5) Acid Treatment Process
The powder was treated in a mix acid of 50% hydrofluoric acid and
70% nitric acid by 1:1. The suspension liquid was changed during
the treatment from deep green to vivid green. Thereafter,
.beta.-type fluorescent substance powder was obtained by washing
with water and drying. FIG. 4 shows a scanning electron microscope
(SEM) picture.
The resulting .beta.-type fluorescent substance powder was
subjected to a minute powder removing treatment by a wet
precipitation method.
The fluorescent substance powder of 10 g was dispersed sufficiently
in 500 mL of distilled water where sodium hexametaphosphate had
been added as a dispersing agent, then the mixture was transferred
to a container of 80 mm in inner diameter and 140 mm in height,
allowed to stand still for 50 minutes, and supernatant solution of
90 mm from the water surface was removed. Hexametaphosphoric acid
aqueous solution was added again and dispersed, and the mixture was
allowed to stand still for a predetermined time, then supernatant
solution was removed, and such operation was repeated until
supernatant solution became transparent. Thereafter, precipitate
was collected by filtration, and washed sufficiently with water to
remove the dispersing agent, and dried to obtain .beta.-type
fluorescent substance powder from which minute powders were
removed.
Comparative Example 1
The treatment was conducted to obtain fluorescent substance powder
in the same treatment process and condition as in Example 1 except
that a high-temperature annealing process was omitted. Namely,
.beta.-type fluorescent substance powder was produced by a method
including "burning process," "argon annealing process," and "acid
treatment process." FIG. 5 shows a scanning electron microscope
(SEM) picture after acid treatment.
It can be seen that a .beta.-type fluorescent substance powder
particle (Example 1) shown in FIG. 4 has a more roundish surface
than a .beta.-type fluorescent substance powder particle
(Comparative Example 1) of FIG. 5.
Particle sizes of the ground powder ground by an ultrasonic jet,
.beta.-type fluorescent substance powder after acid treatment of
Example 1, and .beta.-type fluorescent substance powder after acid
treatment of Comparative Example 1 were measured using a particle
size distribution measuring apparatus of a laser diffraction
scattering method (Beckman Coulter LS230). The particle size
distribution is shown in FIG. 6. It can be seen that the particle
diameter becomes larger by conducting both high-temperature
annealing process and argon annealing process than that by an argon
annealing process alone.
In regard to the .beta.-type fluorescent substance powder obtained
after each process in Example 1 and Comparative Example 1, the
amount of crystal defects was measured using an electron spin
resonator (ESR). The measuring results are shown in Table 1 and
FIG. 7.
TABLE-US-00001 TABLE 1 Amount of crystal defects Amount of Sample
name (spins/g) Eu.sup.2+ (a.u.) Burned powder 2.48E+17 62.99
Jet-milled powder 3.45E+17 68.37 Acid-treated powder 9.03E+16 64.63
(only argon anneal) Acid-treated powder 6.20E+16 62.41
(high-temperature treatment + argon anneal)
From Table 1 and FIG. 7, it can be seen that the amount of crystal
defects can be decreased by an argon annealing process alone.
Moreover, by conducting both high-temperature annealing process and
argon annealing process, it can be seen that the amount of crystal
defects can be further decreased. The decreasing effect on the
amount of crystal defects by conducting the high-temperature
annealing process in addition to the argon annealing process became
more remarkable particularly after acid treatment. On the other
hand, there was no significant change in the amount of
europium.
The elemental compositions of the .beta.-type fluorescent substance
powder after acid treatment of Example 1 and of the .beta.-type
fluorescent substance powder after acid treatment of Comparative
Example 1 were measured. For measurement of oxygen, oxygen/nitrogen
analysis equipment (manufactured by Horiba, Ltd., EMGA-920) was
used. For measurement of europium, aluminum and silicon, a
high-frequency inductive coupled plasma emission spectrophotometer
(Spectro Corporation, Ciros) was used. The results are shown in
Table 2.
TABLE-US-00002 TABLE 2 High-temperature Argon anneal anneal + argon
Sample alone anneal Amount of O (wt %) 1.11 1.00 Amount of Eu (wt
%) 0.41 0.48 Amount of Al (wt %) 1.95 2.06 Amount of Si (wt %) 58.3
62.2
It can be seen that via high-temperature annealing process and
argon annealing process, the amount of oxygen is decreased in
comparison with an argon annealing process alone.
Luminescence intensity of the .beta.-type fluorescent substance
powder obtained in Example 1 and Comparative Example 1 was measured
by a fluorescence spectrophotometer (manufactured by Hitachi
High-Technologies Co., Ltd., "F4500"). The luminescence intensity
was evaluated as follows. Fluorescent substance powder was first
filled in a concave cell such that the surface becomes flat, and an
integrating sphere was equipped. To this integrating sphere,
monochromatic light dispersed into a predetermined wavelength was
introduced via optical fiber from a luminous source (Xe lamp). This
monochromic light was used as an excitation source, a fluorescent
substance sample was irradiated, and spectra of fluorescent light
and reflected light of the sample were measured using a
spectrophotometer. In the present Example, blue light of 455 nm
wavelength was used as monochromatic light. Additionally, the
luminescence intensity was expressed by a relative peak strength
(%) when luminescence intensity of YAG:Ce (P46Y3; Kasei Optonix
Co., Ltd.) was 100%. The results are shown in Table 3 and FIG.
8.
TABLE-US-00003 TABLE 3 Comparative Excitation wavelength: 455 nm
Example 1 Example 1 Relative peak strength (%) 221 203
From Table 3 and FIG. 8, it can be seen that luminescence intensity
is improved by conducting the high-temperature annealing process
and argon gas process together.
Example 2
There is shown an example where silicon powder was used in Example
2 in place of silicon nitride powder of Example 1.
(1) Preparation of Raw Material Powder for Eu-containing .beta.
Sialon
Using a mortar and a pestle made of silicon nitride burned
substance, there were mixed 96.41 mass % of silicon powder (purity
99.999% or more, -45 .mu.m, manufactured by Pure Chemical Co.,
Ltd.), 1.16 mass % of aluminum nitride powder (manufactured by
Tokuyama Corporation, E grade), and 2.43 mass % of europium oxide
powder (manufactured by Shin-Etsu Chemical Co., Ltd., RU grade),
and further all passed through a sieve of 250 .mu.m opening for
removing aggregation, thereby to obtain raw material-mixed
powder.
(2) Nitriding Process
The raw material-mixed powder was filled in a cylindrical container
made of boron nitride of diameter 40 mm.times.height 30 mm with a
lid (manufactured by Denki Kagaku Kogyo Kabushiki Kaisha, "N-1"
grade), and it was heat-treated in an electric furnace with a
carbon heater in a pressured nitrogen atmosphere of 0.48 MPa at
1550.degree. C. for 8 hours. Additionally, the rate of temperature
increase in heating was set to 20.degree. C./min from room
temperature to 1200.degree. C. and 0.5.degree. C./min from 1200 to
1500.degree. C. The resulting product was clumpy, and this was
ground using a mortar and a pestle made of silicon nitride burned
substance. The ground powder was classified by a sieve of 45 .mu.m
opening, and the powder of 45 .mu.m or less was used as
Eu-activated aluminum-containing silicon nitride powder for
synthesizing a fluorescent substance. Further, the Eu-activated
aluminum-containing silicon nitride powder obtained was all passed
through a sieve of 250 .mu.m opening, obtaining raw material-mixed
powder for a .beta.-type sialon fluorescent substance.
(3) Burning Process
The raw material-mixed powder for a .beta.-type sialon fluorescent
substance was filled in a cylindrical container made of boron
nitride of diameter 60 mm.times.height 30 mm with a lid
(manufactured by Denki Kagaku Kogyo Kabushiki Kaisha, "N-1" grade),
and it was heat-treated in an electric furnace with a carbon heater
in a pressured nitrogen atmosphere of 0.8 MPa at 2000.degree. C.
for 8 hours. The resulting product was a green lump being loosely
aggregated, and after cooling to room temperature, it was able to
be flaked gently by a hand wearing a clean rubber glove. In this
way, after being crushed to a slight degree, it was passed through
a sieve of 45 .mu.m opening.
(4) High-temperature Annealing Process
The fluorescent substance powder was filled in a cylindrical
container made of boron nitride of diameter 60 mm.times.height 30
mm with a lid (manufactured by Denki Kagaku Kogyo Kabushiki Kaisha,
"N-1" grade), and it was heat-treated again in an electric furnace
with a carbon heater in a nitrogen atmosphere of atmospheric
pressure at 1800.degree. C. for 8 hours.
(5) Argon Annealing Process
The fluorescent substance powder obtained was heat-treated in an
electric furnace with a carbon heater in an argon atmosphere of
atmospheric pressure at 1400.degree. C. for 8 hours.
(6) Acid Treatment Process
The powder was heat-treated in a mix acid of 50% hydrofluoric acid
and 70% nitric acid by 1:1 at 75.degree. C., thereafter, treated,
filtered, washed with water and dried in the same manner as in
Example 1, obtaining .beta.-type fluorescent substance powder.
Comparative Example 2
The treatment was conducted to obtain fluorescent substance powder
in the same treatment process and condition as in Example 2 except
that a high-temperature annealing process and an argon annealing
process were omitted.
Comparative Example 3
The treatment was conducted to obtain fluorescent substance powder
in the same treatment process and condition as in Example 2 except
that a high-temperature annealing process was omitted.
Using a xenon lamp light source dispersed to excitation light,
luminescence intensity was measured in the same condition as in
Example 1. The results are shown in Table 4.
TABLE-US-00004 TABLE 4 Comparative Comparative Excitation
wavelength: 455 nm Example 2 Example 2 Example 3 Relative peak
strength (%) 170 159 145
It can be seen that luminescence intensity is improved by treatment
in a high-temperature annealing process. It can also be seen that
luminescence intensity is further improved by combination of a
high-temperature annealing process with an argon annealing
process.
The present invention has been described on the basis of Example,
but this Example is only exemplification, those in the art
understand that various modifications are possible and such
modifications are within the scope of the present invention.
Although a few embodiments of the present invention have been shown
and described, it would be appreciated by those skilled in the art
that changes may be made in this embodiment without departing from
the principles and spirit of the invention, the scope of which is
defined in the claims and their equivalents.
* * * * *